"need to narrow" is correct and can be used in written English.
Example: In order to fully understand the topic, we need to narrow our focus and only consider the most relevant information.
Democrats need to narrow or reverse that margin.
Next you need to narrow down your search to courses that are within your budget.
DB: We would need to narrow down the number of SNPs associated with a particular disease.
How do they get the information they need to narrow their choices?
You don't need to narrow the list to 25 if we are talking about general matters of philosophy.
That said, we library-types, we information professionals, we decision makers, and perhaps we citizens need to narrow open gov to make it work for us.
We need to narrow down climate sensitivity from multiple lines of evidence, and there are many remaining uncertainties regardless of approach.
We'll tell them that we need to narrow the team down, and get the key people involved — the ones who own the project.
Human rights groups that call for this kind of intervention need to narrow the gap between high moralism and on-the-ground reality.
If you're pretty sure you want to do medicine or engineering, then you can stop agonising: you need to narrow, not widen, your subject choice.
We also need to narrow the murky and awkward military offense of "aiding the enemy" into a time of war offense and restrict its application to military personnel.
